Syenite
Alkali feldspar-rich intrusive rock (quartz-poor)
A coarse-grained intrusive igneous rock dominated by alkali feldspar with little or no quartz.
- Mohs hardness
- 6-6.5 (rock aggregate)
- Color
- Grey, pink, reddish to white
- Type
- igneous
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Overview
Syenite is a coarse-grained, light-colored intrusive igneous rock composed mainly of alkali feldspar, with minor amphibole, pyroxene, biotite, and very little or no quartz. It resembles granite but is distinguished by its scarcity of quartz.
The rock takes its name from Syene (modern Aswan, Egypt), though the rock originally quarried there was actually a granite. Syenite varies in color from grey and white to attractive pink and reddish tones depending on its feldspar.
Nepheline syenite, a quartz-free variety containing the feldspathoid nepheline, is an industrially important subtype.
Formation & geology
Syenite forms when alkali-rich, silica-undersaturated magma cools slowly deep within the Earth's crust, allowing large interlocking crystals to grow. The low silica content prevents abundant quartz from crystallizing, so feldspars dominate instead.
It typically occurs in plutons, dikes, and intrusive complexes associated with continental rifting and alkaline magmatism. Notable occurrences include Norway (where larvikite is a famous variety), the Kola Peninsula of Russia, Ontario in Canada, and Arkansas in the United States.
How to identify it
Look for a coarse-grained, light-colored rock dominated by blocky feldspar crystals with relatively few dark minerals and little to no glassy quartz. Color ranges from grey and white to pink or red.
The key field test is the near-absence of quartz: granite contains abundant glassy grey quartz, while syenite is feldspar-dominated. A hand lens helps confirm the lack of quartz.
Look-alikes include granite (has visible quartz) and monzonite (more plagioclase). Larvikite, a syenite, shows a distinctive blue-grey iridescent schiller.
Uses & significance
Syenite is used as a durable dimension and ornamental stone for countertops, facades, flooring, and monuments; the iridescent larvikite variety is especially prized as 'blue granite' in architecture.
Nepheline syenite is industrially valuable as a quartz-free source of alumina and alkalis used in glass and ceramic manufacturing, where its low silica and high feldspar content improve melting. Crushed syenite also serves as construction aggregate. It has minimal use as a gemstone but is a handsome decorative material.
Frequently asked questions
What is the difference between syenite and granite?
Both are coarse-grained intrusive rocks, but granite contains abundant quartz while syenite has little or none, being dominated by alkali feldspar.
Is larvikite a syenite?
Yes. Larvikite is a feldspar-rich syenite from Norway famous for its blue-grey iridescent schiller, often sold as 'blue granite.'
What is nepheline syenite used for?
It is a quartz-free industrial mineral used in glass and ceramic production as a source of alumina and alkalis that lower the melting temperature.
Where does syenite form?
It crystallizes slowly from alkaline, silica-poor magma deep in the crust, often in rift settings and alkaline intrusive complexes.
Syenite guides
In-depth guides for identifying, valuing, and understanding Syenite.
Syenite identified by the community
Real specimens identified with Rock Identifier.
